Furnaces for generating zinc vapors



Se t. 4, 1956 R. A. WlLKlNS 2,761,672

FURNACES FOR GENERATING ZINC VAPORS Fild April 13, 1955 3 Sheets-Sheet l INVENTOR Sept. 4, 1956 R. A. WlLKlNS 2,761,572

FURNACES FOR GENERATING zmc VAPORS Filed April 13, 1955 s shee'ts-shez 2 lA/VEN TOR 4.45%? IW' T'YSI Sept. 4,1956 R. A. WlLKlNS FURNACES FOR GENERATING ZINC VAPORS 3 Sheets-Sheet 3 Filed April 13, 1955 INVENTOR R/CHA A. WlLK/N /6..

1- I Arfys.

United States Patent "ice FOR GENERATING ZINC VAPORS Richard .A. .WilkinsyRome, N. Y., ,assignor to Revere ,Copper and ,Brassslncorporated, Rome, N. Y a cor- PQration ,of Maryland Application-April m, 1953, Serial No. 348,433

t8 Claims. .(Cl.t26624) My invention relates to furnaces, particularly to electric'furnaces for-generating zinc vapors from zinciferous -mater ial-and meltingthe residue -of the zinciferous material and discharging it therefrom.

Furnaees according to the invention are particularly applicable for-performing the operations disclosed by pending joint application of applicant and Kenneth A. Phillips, 'Serial Number 220,574, filed April 12, 1951, andby United states patenttoFrank -F. Poland 2,463,468, granted *Ivlareh l, 1949,. and from this aspect may be considered as constituting improvements inthe furnaces disclosed by said application and patent.

In the drawings:

Fig. *1 is.a-longitudina-l section'of-a furnace constructed according to -the "invention;

Figs. 2, 3 and '4 are sections on the lines 2-2,"33 and -4+4, respectively, of Fig. 1;

Fig. 5 is a fragment of a longitudinal section of a modified form of furnace;

Fig. 6"isia fragment of a longitudinal-section of a further modified form a of furnace; and

Fig. 7 is a fragment .of a longitudinal "section of astill further modified-form of furnace.

l he furnacetaceording'toFigs. 'l to 4 is a'zinc smelting furnace generally like that disclosed-by-theabove mentioned pending application. *It comprises an exterior air-tight box-like casing, preferably-of steel,-'having the :opposite side walls -1 and 3, bottom wall 5,-and -re- -rnovablei top wall orcover 7,'the -joint between the top wall andzsidemallsbe'ing rendered air-tightby "the seal 9:.extending entirely around the furnace.

ilnteriorly :the furnace is formed to provide a furnace chamberfill idivided into uppenand lower portions by a pantitionformed of graphite bars =13. The portion of the chamber .:'below "the partition constitutes the -labora .tory' "and zinc vapor -space. of the c'hamberyfrom which latter the zinc vapors discharge throughacondu'it .to a.c.ondenser (not shown) where the vapors are-condensed tofiliquid zinc.

Above the partition formed {by the bars -13 is suspended in insulated relation to the rest of the furnace a heating grid comprising graphite electric heating resistors 17, the .terminals:il9 ofmthe grid :being locatedat the exterior .Ofthe casing.

The side walls of the-portion of the furnace casing surrounding the vapor space of the furnace cham'ber are operatively linedwith brickwork or the like comprising the :inner courses of 'bricks or blocks 21 -of highly refractory materialsuchtas alumina, intermediate courses of insulating firebrickz23, and outer courses of ordinary firebrickQS, there being interposed between -the-latter and the, casing va layer 27 of refractory resilient lagging to take ,=up the expansion of the brickwork when it is heated.

Thebottomzwall of thecasing is operatively lined by briekworkpr the like, the flowerportion-of which comprises the. superimposed courses of firebrick 29, on which courses the brickwdrk forming the side walls of the fur- 'nace chamber rests.

Supported on the coursesl'offirebrick 29 between" the" side walls of :thefurnacechamber and forming the upper "portion'of the bottomwzillof the furnace is a layer of wedge-shaped bricks or blocks 31 and 33 preferably of alumina or 'hardcarb'onfthe'bricks or blocks '33 being of 'less thickness "vertically"than'the blocks 31 so as to *form' a-pit 35 at the, left hand side'of the furnace chamber as viewedin Fig. 1; Asxshown, the'course-of blocks 33 does not extendentirely'toithe adjacent side wall of the furnace, thespace'between the two beingformedby courses of readily'replaceable wear resistant blocks 37, formedof 'heat'refractory material such as hard carbon or aluminayone ofthese blocks as shown being laid to forma taphole 39 communicating with the 'pit adjacentits bottom.

As shown, one of theside walls of 'the furnace 'is provided'with a downwardly inclined'charging port 41 having a metallic extension '43 at-the exterior of'the'furnace carried by the adjacent sidewalls of the furnace'casing. At its outer end this extension is formed to provide a box-like enlargement 45 having a normally closed 'hinged air-tight lid 47, which latter -may be opened 'to permit the furnace to be-charged with granular 'oxidized zincifi erousmaterialmixed with granulated reaction carbon as, :for-example, roasted zinc oreconcentrate "mixed with broken up coke'o'f relatively-small particle size. "This -mi-xture forms --o11 =the bottom of the chamber af-OnE'jSldB of-the 'pit 35 *a mass of -niinture having -a downwardly slopingupper surface 49, the mixture 'being fchargetl from time-to time to -maintainsuch mass.

The heat radiated by theresistors '17 heats the "parti ti'on formedtof the bars 13,*Whichheatisradiateddown- -wardtzon 'the upper-surface of the mass of mixture and into the pit.- This-"heat causes reaction between the 'oxidized z'in'ciferous material and the reactioncarbon at "the uppensloping surface ofthe'charge, to produce iz'inc vapors and gaseous-:reaction products. 'It-also melts'at the upper sloping surface of the charge the-slag from "the mixture, which-slaggravitates down-said:surfaceto thespace between-the lower-edge'of said-"surface and the pitg-andiflows into and collects in "the pit. Inpractice the temperature in the vapor space of the furnace chamber may be --about 32800 *F, while the temperature of the upper sloping surface of the mass of mixture, due tothe endothermic nature of the reactionywill not exceedaboutZS'OO" F. 'The slag in' the p'it, under these conditions,- will be heated to about 2400 Extending through the "side" *wall of the furnace is shown a block 51 provided with a taphole 53 'alignediand 'cornmtmicatingwith thetaphole 39-,'"the 'tap'hole 53"be- =in-g normally closedby 'a removable .plug "55 of known construction. Upon removal of the plug themoltenslag will :discharge through the aligned tapholes 39 and '53 to the-exterior'of the furnace and be caught-by aspout57 for discharging it into aconvenient-receptacle.

The brickwork and the like forming the "side and ib'o't- :tomwalls of the furnaceichamber is'of such thickness with relation to rits heat conductivity-as 'tomaintain the metallic furnace casing at a temperature below that at'wh'ich it will soften, preferably -a temperature "not greater than -about35'0 to 400 F. It will be observed that-the brickwork form'ingthe sidewalls-is exposed to the vapor space of the furnace chamber. Consequentlysuch=vaporunavoidably enters the interstices of the side walls, which walls and the. bottom wall are laid-dry. At an-intermediate portion-of the thickness of saidwalls the-'vaporscom densewto sliquid zinc, and adjacent the met-alcasing such liquidrzinc solidifies, resulting in there being three zones of :zinc in the interstices ofthe .side walls, .1nan1ely,: an inner zone in which the zinc .in1'vaporrform,:an;inter mediate zone in which itis in liquid 1f01'1115a'3l1d5211; outer zone in which it is in solid form. This liquid zinc, it

has been found, percolates downward through the interstices of the side walls to the interstices of the bottom wall, tending, if means are not provided to prevent it, to fill the interstices of the bottom wall intermediate its thickness with liquid zinc, such also seeping into the pit.

Liquid zinc being a good conductor of heat will, if it is pennitted to fill the interstices of the bottom wall and seep into the pit as above described, prevent proper heating of the bottom wall and the slag in the pit. It has been found, for example, that after about twenty-four hours of continued operation of the furnace, it means are not provided for draining the liquid zinc from such interstices and from the pit to a sufliciently low level below the bottom of the pit, the taphole from the pit becomes plugged with solidified slag, and a layer of solidified slag is formed intermediate the height of the pit on the liquid zinc therein, with a layer of liquid slag above the solidified layer thereof. The conductivity of the liquid zinc is such that the slag cannot be effectively melted to clear the taphole or remove the solidified layer of slag in the pit by raising the temperature of the furnace any practical amount. Inserting the usual hand operated bar through the taphole to free it and break the solidified layer of slag in the pit it has been found causes the molten slag above the solidified layer thereof to descend and contact the liquid zinc in the pit and the adjacent interstices of the bottom wall and violently explode the liquid zinc, because the melting point of the liquid slag, which is about 2200 F., is far in excess of the boiling point of zinc. Such explosions are exceedingly dangerous to the operator and result in severe damage to the furnace.

To avoid the above deleterious effects the block 51 is preferably made of highly heat conductive material, such as graphite, so that it will be heated by conduction from the inner hot portions of the furnace walls throughout its extent to a temperature above the melting point of zinc. By providing such block on its under side with a groove 59 opening at its outer end at the exterior of the furnace communication is established between the exterior of the furnace and the portion of the interstices of the bottom wall containing liquid zinc. This groove will therefore serve to drain liquid zinc from such interstices through the zone of solidified zinc adjacent the metal furnace casing to maintain the level of such liquid zinc in said interstices at a sutficiently low level to keep liquid zinc out of the pit and to permit all the slag in the pitand portion of the taphole inwardly of the plug 55 to be heated by radiation from above to such temperatures as will maintain it in molten state during normal operation of the furnace. In practice, after the furnace is in operation for about twenty-four hours, a small stream of liquid zinc will more or less continuously trickle from the outer end of the groove 59. i

The graphite block 51 tends to be heated to incandescence, and to prevent it from burning its outer end is preferably faced with a slab 61 of non-combustible refractory material such as alumina, while the space between the taphole 53 of said block and the plug 55 at the outer end of such space is normally filled with a readily broken away mass of fireclay (not shown).

The operations described by the above mentioned Poland Patent 2,463,468, briefly stated, comprise charging molten zinciferous material containing iron, such as galvanizing dross, at a temperature of about 1300" E, into a furnace chamber wherein it is heated to about 1700 to 2000 F. by radiation from above to evaporate zinc therefrom, the iron precipitating in solid form and collecting at the bottom of the furnace chamber, and, upon this precipitated iron accumulating, the charging and evaporating operations are temporarily discontinued and the furnace temperature raised to heat such iron to a temperature of about 2600 F. for melting it for permitting it to be discharged from the furnace chamber through a suitable normally plugged taphole.

The furnace for performing the operations described by 4 the Poland Patent 2,463,468 may take the form of that illustrated by Fig. 5 which may be identical with that heretofore described except that no pit in the bottom wall of the furnace is provided and means are provided for entering molten charge instead of solid charge into the furnace chamber.

As shown in Fig. 5, one of the side walls of the furnace chamber is provided with a charging port 63 which communicates with a chamber 65 intermediate the height of the latter, this chamber being provided with a partition 67 extending downwardly to a point below the level of the point of communication of the port 63 with said chamber so as to form a trap for preventing escape of zinc vapors from the furnace chamber and entrance of air thereto, the metal in the chamber 65 being maintained in liquid state by a gaseous or liquid fuel torch discharging combustible mixture or fluid into said chamber through the opening 69. The molten dross is charged to the chamber 65, and hence to the port 63, through a passage 71 which communicates with an open top chamher 7 3 into which the molten dross from an exterior source is adapted to be ladled. This construction, for charging molten dross to the furnace chamber, is substantially identical with that described by said patent and need not be further described.

It has been found that collection of liquid zinc in the interstices of the bottom wall of the furnace according to Fig. 5 for performing the operations described in the Poland Patent 2,463,468 acts to prevent the residual iron from being effectively melted when the temperature of the furnace is raised in an attempt to melt such iron. This collection of molten zinc in said interstices may, however, be prevented in exactly the same way as described in connection with the furnace according to Figs. 1 to 4.

It will be understood that the means for preventing an excess of accumulation of molten zinc in the interstices of the bottom wall of the furnace need not be associated with the taphole 53. For example, the opposite end of the furnace from the block 51 of Fig. 5 may be provided, as shown by Fig. 6, with the graphite block 75 identical with the block 51 except that the taphole is omitted, the groove 59 of the block 75 communicating with the interstices of the bottom wall of the furnace and acting in the same way to drain liquid zinc from said interstices as the like groove in the block 51.

It will also be understood that the block 75 of Fig. 6 need not extend entirely through the wall of the furnace chamber, but may terminate short of such wall as indicated by the block 77 of Fig. 7, the block 77 being heated by conduction from the inner hotter portions of the furnace wall to maintain it at a sufficiently high temperature throughout its length to cause the liquid zinc which collects in the groove 79 of said block to be maintained liquid so that it may discharge from said groove to the exterior of the furnace.

The term brickwork is used for convenience of terminology in the appended claims as including bricks, blocks, slabs and other shapes adapted to be laid to form a wall.

It Will be understood that within the scope of the appended claims wide deviations may be made from the forms of the invention herein described without departing from the spirit of the invention.

1 claim:

1. Apparatus for generating zinc vapors from zinciferous material comprising means forming a furnace chamber comprising bottom and lateral walls, heating means above said bottom wall for heating zinciferous material charged to said chamber for generating zinc vapors from such material, discharge means from said chamber for the zinc vapors, the said means forming said chamber having an exterior metal casing which is operatively lined by said bottom and lateral walls, which walls are of such thickness with relation to their heat conductivities as to maintain said casing and the adjacent porbottom wall of said chamber, andmeans for draining-to 1 theexterior of saiducasing liquidzincwhich collects in thfirll'liBI'StlCSS- of-said-bottom wall comprising material vof=J-high heat: conductivity extending through :such wall frornadjacent .said chamber to adjacent said casing form. ing. a drainage-conduit in communicationwith such. interstices;

2. Apparatus according'to'claim l'in-which the means formingthe. conduit-lion draining liquidzinc from the interstices of the. bottom wall comprisesa blo ckrof. graph.- ite grooved on its lower side to form such conduit,-theopen side of such groove communicating with the interstices of saidsbottom wall.

3. Apparatus for-:generatingzinc vapors from zinciferous material comprising means forming a furnace chamber comprising 'bottomandlateral walls, heating means above said bottom wall for heating zinciferous material charged to said chamber for generating zinc vapors from such material, discharge means from said chamber for the zinc vapors, the said means forming said chamber having an exterior metal casing which is operatively lined by said bottom and lateral walls, which walls are of such thickness with relation to their heat conductivities as to maintain said casing and the adjacent portions of said walls at a reduced temperature below the melting point of zinc and comprise brickwork at a side of said chamber and its bottom, the brickwork at the side of said chamber being exposed to the zinc vapor space of said chamber whereby zinc vapors unavoidably enter the interstices of such brickwork and condense to liquid zinc intermediate its thickness and percolate downward through such interstices to those of the brickwork of the bottom wall of said chamber, means forming a taphole communicating with said chamber adjacent the bottom thereof for discharging residue of such zinciferous material therefrom, said last mentioned means comprising material of high heat conductivity extending through said walls from adjacent said chamber to adjacent the exterior of said casing and formed to provide a conduit communicating with the interstices of said bottom wall for draining liquid zinc therefrom.

4. Apparatus for generating zinc vapors from zinciferous material comprising means forming a furnace chamber comprising bottom and lateral walls, heating means above said bottom wall for heating zinciferous material charged to said chamber for generating zinc vapors from such material, discharge means from said chamber for the zinc vapors, the said means forming said chamber having an exterior metal casing which is operatively lined by said bottom and lateral walls, which walls are of such thickness with relation to their heat conductivities as to maintain said casing and the adjacent portions of said walls at a reduced temperature below the melting point of zinc and comprise brickwork at a side of said chamber and its bottom, the brickwork at the side of said chamber being exposed to the zinc vapor space of said chamber whereby zinc vapors unavoidably enter the interstices of such brickwork and condense to liquid zinc intermediate its thickness and percolate downward through such interstices to those of the brickwork of the bottom wall of said chamber, means forming a taphole communicating with said chamber adjacent the bottom thereof for discharging residue of such zinciferous material therefrom, said last mentioned means comprising material of high heat conductivity extending through said walls from adjacent said chamber to adjacent the exterior of said casing and formed to provide on its under side a longitudinally extending groove I the, open: side of which communicates "wit-h'the interstices ef-said bottom wallifort draining liquid zinc therefrom. t

5. Apparatus-ion generating zine vapors -fromzinciferous" material comprising means-forminga furnace chamber" comprising bottom and: lateral walls, heating meansabove said .bottom wall for: heating (ZiIlClfGl'OllS material charged to said chamber for generating Zinc vapors. from such material; r discharge 1 means from said chamber for the zine-vapors, the said-means forming said chamber having an exterior: metal casing which. is toperatively lined by said. bottom :and lateral -.-wal1s', which walls: are- -ofsuch: thickness with-relation to their: heat conductivities as tomaintain saidcasingzandithe adjacent portions of said:walls at areduced/temperature below the melting'point of zincwand COIIIPI'lSflbIlOkWOIk: at a side: of said chamber and its bottom; the brickworkrat .thezsidefof said chamber: being exposed to the r zinc ivaporrspace :of said: chamber whereby: zincvapors :unavoidably'enterthe interstices: of such brickwork and: condense to liquid zinc intermediate. its ;thickness 1 and). percolate "downward through such interstices to thoseof' thebrickworkuof the bottom walbofsaid-chamber, .meansz'forminga taphole communicating :with :said :chamber adjacent sthe bottom thereof for dischargingresidue. of .suchzinciferous material therefrom; said .last merrtionectrmeans 'comprising'wmas terial of graphite extending through said walls from adjacent said chamber to adjacent the exterior of said casing and formed to provide a conduit communicating with the interstices of said bottom wall for draining liquid zinc therefrom.

6. Apparatus for generating zinc vapors from zinciferous material comprising means forming a furnace chamber comprising bottom and lateral walls, heating means above said bottom wall for heating zinciferous material charged to said chamber for generating zinc vapors from such material, discharge means from said chamber for the zinc vapors, the said means forming said chamber having an exterior metal casing which is operatively lined by said bottom and lateral walls, which walls are of such thickness with relation to their heat conductivities as to maintain said casing and the adjacent portions of said Walls at a reduced temperature below the melting point of zinc and comprise brickwork at a side of said chamber and its bottom, the brickwork at the side of said chamber being exposed to the zinc vapor space of said chamber whereby zinc vapors unavoidably enter the interstices of such brickwork and condense to liquid zinc intermediate its thickness and percolate downward through such interstices to those of the brickwork of the bottom wall of said chamber, means forming a taphole communicating with said chamber adjacent the bottom thereof for discharging residue of such zinciferous material therefrom, said last mentioned means comprising material of graphite extending through said walls from adjacent said chamber to adjacent the exterior of said casing and formed to provide on its under side a longitudinally extending groove the open side of which communicates with the interstices of said bottom wall for draining liquid zinc therefrom.

7. Zinc smelting apparatus comprising means forming a furnace chamber having bottom and lateral walls, means for charging oxidized Zinciferous material mixed with reaction carbon to said chamber to form and maintain on the upper surface of said bottom wall a mass of such charge having an upper surface which slopes downwardly heating means above said bottom wall for radiating heat downward on such charge for generating zinc vapors therefrom and causing molten slag from said charge to gravitate down said sloping surface, said bottom wall being formed to provide a pit for receiving such slag, the said means forming said chamber having an exterior metal casing which is operatively lined by said walls, which walls are of such thickness with relation to their heat conductivities as to maintain said casing and the adjacent portions of said walls at a reduced temperature below the melting point of zinc and comprise brickwork at the side of said chamber and its bottom, the brickwork at the side of said chamber being exposed to the zinc vapor space of said chamber whereby zinc vapors unavoidably enter the interstices of such brickwork and condense to liquid zinc intermediate its thickness and percolate downward through such interstices to those of the brickwork of the bottom wall of said chamber, means forming a taphole for discharging molten slag from said pit to the exterior of said casing, and separate means for draining to the exterior of said casing liquid zinc which collects in the interstices of said bottom wall comprising material of high heat conductivity extending through such wall from adjacent said chamber to adjacent said casing forming a drainage conduit in communication with such interstices.

8. Zinc smelting apparatus comprising means forming a furnace chamber having bottom and lateral walls, means for charging oxidized Zinciferous material mixed with reaction carbon to said chamber to form and maintain on the upper surface of said bottom wall a mass of such charge having an upper surface which slopes downwardly, heating means above said bottom wall for radiating heat downward on such charge for generating zinc vapors therefrom and causing molten slag from said charge to gravitate down said sloping surface, said bottom wall being formed to provide a pit for receiving such slag, the said means forming said chamber having an exterior metal casing which is operatively lined by said walls, which walls are of such thickness with relation to their heat conductivities as to maintain said casing and the adjacent portions of said walls at a reduced temperature below the melting point of zinc and comprise brickwork at the side of said chamber and its bottom, the brickwork at the side of said chamber being exposed to the zinc vapor space of said chamber whereby zinc vapors unavoidably enter the interstices of such brickwork and condense to liquid zinc intermediate its thickness and percolate downward through such insterstices to those of the brickwork of the bottom wall of said chamber, and means forming a taphole for discharging molten slag from said pit to the exterior of said casing comprising material of high heat conductivity extending from adjacent a side wall of said pit to adjacent said casing and formed to provide a groove the open side of which communicates with the interstices of said bot tom wall for draining liquid zinc therefrom for discharge at the exterior of said casing.

References Cited in the file of this patent UNITED STATES PATENTS 

1. APPARATUS FOR GENERATING ZINC VAPORS FROM ZINCIFEROUS MATERIAL COMPRISING MEANS FORMING A FURNACE CHAMBER COMPRISING BOTTOM AND LATERAL WALLS, HEATING MEANS ABOVE SAID BOTTOM WALL FOR HEATING ZINCIFEROUS MATERIAL CHARGED TO SAID CHAMBER FOR GENERATING ZINC VAPORS FROM SUCH MATERIAL, DISCHARGE MEANS FROM SAID CHAMBER FOR THE ZINC VAPORS, THE SAID MEANS FORMING SAID CHAMBER HAVING AN EXTERIOR METAL CASING WHICH IS OPERATIVELY LINED BY SAID BOTTOM AND LATERAL WALLS, WHICH WALLS ARE OF SUCH THICKNESS WITH RELATION TO THEIR HEAT CONDUCTIVITIES AS TO MAINTAIN SAID CASING AND THE ADJACENT PORTIONS OF SAID WALLS AT A REDUCED TEMPERATURE BELOW THE MELTING POINT OF ZINC AND COMPRISE BRICKWORK AT THE SIDE OF SAID CHAMBER AND ITS BOTTOM, THE BRICKWORK AT THE SIDE OF SAID CHAMBER BEING EXPOSED TO THE ZINC VAPOR SPACE OF SAID CHAMBER WHEREBY ZINC VAPORS UNAVOIDABLY ENTER THE INTERSTICES OF SUCH BRICKWORK AND CONDENSE TO LIQUID ZINC INTERMEDIATE ITS THICKNESS AND PERCOLATE DOWNWARD THROUGH SUCH INTERISTICES TO THOSE OF THE BRICKWORK OF THE BOTTOM WALL OF SAID CHAMBER, AND MEANS FOR DRAINING TO THE EXTERIOR OF SAID CASING LIQUID ZINC WHICH COLLECTS IN THE INTERSTICES OF SAID BOTTOM WALL COMPRISING MATERIAL OF HIGH HEAT CONDUCTIVELY EXTENDING THROUGH SUCH WALL FROM ADJACENT SAID CHAMBER TO ADJACENT SAID CASING FORMING A DRAINAGE CONDUIT IN COMMUNICATION WITH SUCH INTERSTICES. 